The human interleukin-2 receptor is being studied to understand critical components of the T cell immune response in normal and neoplastic cells. Following T-cell activation, IL-2 and IL-2 receptors are induced; the magnitude and duration of the T-cell immune response is controlled by the amount of IL-2 produced, the levels of receptors expressed, and the time course of these events. Three chains of the IL- 2 receptor exist, IL-2Ra, IL-2Rb, and gc, with IL-2Ra and IL-2Rb being significantly regulated at the level of transcription. The laboratory has focused primarily on the types of signals induced by IL-2, particularly the activation of STAT proteins, and the mechanism of regulating IL-2Ra gene expression in response to mitogen and IL-2. Considerable progress has been made in analyzing the STAT proteins (signal transducers and activators of transcription) induced by IL-2. IL-2 can activate both Stat5a and Stat5b (two closely related proteins with >90% amino acid identity) in fresh peripheral blood lymphocytes (PBL) and additionally activates Stat3 in PBL preactivated with phytohemagglutinin. Consistent with the presence of an IL-2 response element previously characterized in the 5? regulatory region of the IL- 2Ra gene, it was reported that like Stat5a knockout mice, Stat5b knockout mice are defective in IL-2-induced IL-2Ra expression. However, these mice have a greater defect than is seen with Stat5a knockout mice in terms of proliferation, as it could not be overcome by doses of IL-2 high enough to titrate intermediate affinity IL-2 receptors. Stat5b knockout mice also exhibit a substantial defect in the proliferative and cytolytic activities of natural killer cells. These studies substantially extend our understanding of the molecular basis for IL-2 upregulation of the IL-2Ra gene and partially clarify the roles of Stat5a and Stat5b. Other transgenic approaches are being used to further investigate distinctive vs. overlapping roles of Stat5a and Stat5b. An additional regulatory element in the IL-2Ra gene has now been identified. Stat5a and Stat5b proteins purified from a baculovirus expression system were used in a binding site-selection analysis. This has revealed that both Stat5a and Stat5b dimers bind to similar TTCN3GAA motifs, whereas Stat5a dimers exhibit binding to a larger repertoire of sites than was expected. It was also demonstrated that Stat5 proteins regulate the IL-2 response element in the IL-2Ra gene by former tetramers and that such tetramerization is vital for high affinity binding of Stat5. One gene product, Nmi (N-Myc interactor), was found to interact with Stat5b in a yeast two hybrid analysis and the ability of Stat5 to associate with the general transcriptional coactivators, CBP and p300, has been investigated. The lab has also worked to set up systems to define the role of serine phosphorylation of substrates in response to IL-2. Together, these studies substantially enhance our understanding of the basis for IL-2R expression as well as IL-2-dependent gene regulation. - IL-2, IL-2 receptor, Stat5a, Stat5b, IL-2Ra gene, peripheral blood lymphocytes, knockout mice